Transgenic Plants Resistant To Non-Protein Amino Acids

ABSTRACT

Transgenic plants resistant to bio-herbicides, particularly to phytotoxic non-protein amino acids including the meta-tyrosine (m-tyrosine) amino acid analog and salts thereof, means and methods for producing the transgenic plants.

FIELD OF THE INVENTION

The present invention relates to transgenic plants resistant tobio-herbicides, particularly to phytotoxic non-protein amino acidsincluding meta-tyrosine amino acid analog and salts thereof and tomethods for producing the transgenic plants.

BACKGROUND OF THE INVENTION

“Allelopathy” is a term referring to an effect (inhibitory orstimulatory) of a plant on surrounding species by chemicals(allelochemicals) released by the plant into the environment. Theallelochemicals are usually secondary metabolites that can besynthesized in any of the plant parts, and can have beneficial (positiveallelopathy) or detrimental (negative allelopathy) effects on the targetorganisms. Allelochemicals are not required for the metabolism (i.e.growth, development and reproduction) of the allelopathic (resistant)plant, but interfere with vital metabolic pathways of non-resistantspecies providing relative advantage to the resistant plant. Theallelopathic effect was realized already in the Greek era. The advantageof allelopathic effect of several widely used crop plants such as wheat,rice and cucumber is known and used. Lately the awareness of thepotential to implement this phenomenon in weed management has risen.Among other observed allelochemicals, meta-tyrosine, which showspromising phytotoxic activity, was proposed as possible environmentalfriendly weed suppressor (Bertin C. et al., 2007. Proceedings of theNational Academy of Sciences of U.S.A 104, 16964-16969).

Meta-tyrosine (m-Tyr) is naturally occurring non-protein amino acid. Itcan be produced by two possible synthesis routes: through the pathway ofdopamine synthesis or by oxidation of phenylalanine by reactive oxygenspecies. The m-Tyr, an isomer of the common protein amino acid tyrosine(p-tyrosine), has been found in Euphorbia myrsinites (donkey tailspurge) and some fescue species. Originating from plants, m-Tyr wasfound to be toxic to a broad spectrum of species. At a concentration aslow as 2 μM added to an agar medium m-Tyr inhibits Arabidopsis thalianaroot growth by 50%, and completely prevents seed germination at aconcentration of 50 μM (Bertin C. et al. 2007, ibid).

The appearance of m-tyrosine (m-Tyr) along with o-tyrosine (o-Tyr) andL-dopa within proteins has been widely used as an index for the degreeof oxidative damage caused to the proteins. It has been demonstratedthat in eukaryotic cells, certain exogenously supplied oxidized aminoacids, including m-Tyr, can be incorporated into proteins by the cellbiosynthetic pathways rather than via chemical reactions. It istherefore likely that in many cases, amino acids damaged in vivo areavailable for de-novo synthesis of proteins. This theory is supported bythe finding that exposure to m-Tyr results in growth inhibition of awide range of plant species including commercially important monocot anddicot crop plants. It has been further suggested that the phytotoxicityof m-Tyr is caused by its incorporation into proteins in place ofphenylalanine during protein synthesis.

Phenylalanyl-tRNA synthetase (PheRS) belongs to the family ofaminoacyl-tRNA synthetases (aaRS), which play critical role intranslation of the genetic code. The aaRSs ensure the fidelity of thetranslation of the genetic code, covalently attaching appropriate aminoacids to the corresponding nucleic acid adaptor molecules—tRNA. TheaaRSs are a notoriously diverse family of enzymes, varying considerablyin primary sequence, subunit size and oligomeric organization.Phylogenetic and structural analyses reveal three major forms of PheRS:a) heterotetrameric (αβ)2 bacterial PheRS; b) heterotetrameric (αβ)2archaeal/eukaryotic-cytoplasmic PheRS; and c) monomeric mitochondrialPheRS.

The accuracy of aminoacylation reaction promoted by aaRSs, and PheRS inparticular, is based on precise recognition of the amino acid substrate.However, due to stereo-chemical similarity shared by several aminoacids, mistakes in recognition occur. Phenylalanine (Phe) and Tyrosine(Tyr) are distinguished by only one hydroxyl group at the aromatic ringand thus differentiation between Phe and Tyr is not always fulfilled.PheRS successfully differentiates between these amino acids with amistake rate of 1:1000. A higher level of total accuracy of proteinbiosynthesis is ensured by an editing activity of PheRS along with otheraaRSs. The editing activity is associated with the specific site, wheremisacylated tRNAs are hydrolyzed.

Some of the inventors of the present invention and co-workersinvestigated the ability of PheRSs from various sources, includingbacterial (Thermus thermophilus (Tt) and Escherichia coli (Ec)) andhuman (cytosolic (Hsct) and mitochondrial (Hsmt)) source to activatem-Tyr and attach it to tRNA^(Phe) (Klipcan, L., et al., 2009.Proceedings of the National Academy of Sciences U.S.A 106, 11045-11048).The radical-damaged amino acid is activated by these enzymes as assayedby ATP hydrolysis. Steady-state kinetic measurements of aminoacylation(assayed by means of acidic gel electrophoresis) revealed no mischargingof tRNA^(Phe) with m-Tyr by bacterial PheRS (FIG. 1). This observationserves as an indication for the efficiency of the editing mechanism.Moreover, when the bacterial PheRS is incubated with preloadedm-Tyr-tRNA^(Phe), the m-Tyr was deacylated from the tRNA providing theevidence for the so-called trans-editing activity (Ling, J. et al.,2007. Proceedings of the National Academy of Sciences U.S.A 104, 72-77).On the contrary, the mitochondrial enzyme could stably synthesizem-Tyr-tRNA^(Phe). The HsmtPheRS does not contain editing domain andtherefore cannot deacylate the non cognate amino acids from tRNA (Roy,H. et al., 2005. The Journal of biological chemistry 280, 38186-38192;Kotik-Kogan, O. et al., 2005. Structure 13, 1799-1807), providing thepath for these residues to be incorporated into the protein polypeptidechains. Analysis of kinetic parameters of tRNA^(Phe) aminoacylationshows that the catalytic efficiency (k_(cat)/K_(m)) of m-Tyr attachmentby HsmtPheRS is only fivefold lower than that of the correct amino acid,primarily due to a higher K_(m) value. Relatively high catalyticactivity of mitochondrial PheRS toward m-Tyr and lack of editingactivity can explain the profound toxic effect of m-Tyr has on plants.In plants, more than 150 proteins are expressed in the mitochondria andchloroplasts, and the monomeric phenylalanyl-tRNA synthetase (PheRS),present in plant organelles is closely resembled to the humanmitochondrial PheRS. Thus, incorporation of m-Tyr instead of Phe intoorganellar proteins results in a large number of damaged proteins,therefore reducing cell viability. The moderate toxicity of m-Tyr tomammalian cells can be explained by the fact that in these cells amitochondrion encodes only 13 proteins.

Reducing the use of herbicides has become a significant target inkeeping sustainable agriculture and landscape management. There is anongoing effort in developing biological and organic approaches for weedcontrol that can effectively replace the use of hazardous chemicals. Atthe same time, efforts are made to have means and methods for protectingcrop plants from the phytotoxic compounds taking the molecular geneticsapproach and/or employing natural products.

For example, International PCT Application Publication No.WO/2005/077171 discloses methods for protecting plants from herbicideinjury and damage by coating or priming seeds with one or more aminoacids to confer tolerance to herbicides that disrupt production of theamino acids by a plant treated with the herbicide.

The significant toxicity of m-Tyr to plants but the reduced effect onfungi, mammals or bacteria has led to its development as abio-herbicide. U.S. Patent Application Publication No. 20080261815discloses methods of using m-tyrosine compounds from Festuca species forinhibiting weed growth and enhancing growth of non-weed plants, andfurther discloses methods of identifying plants having herbicidalproperties. The shortage of the use of m-Tyrosine as a bioherbicide isthat it is toxic not only to weeds but also to crop plants.

There is a recognized need for it would be highly effective to havemeans for producing transgenic plants, particularly crop or ornamentalplants that are resistant to phytotoxic allelochemical, for example tonon-protein amino acids including m-Tyrosine.

SUMMARY OF THE INVENTION

The present invention provides means and methods for conferring totransgenic plants resistance to the presence of phytotoxic non-proteinamino acids in the plant growth medium. The present invention furtherprovides transgenic plants resistant to phytotoxic non-protein aminoacids, particularly to meta-tyrosine (m-Tyr) and salts thereof.

The present invention is based in part on the unexpected discovery thatexpressing bacterial phenylalanyl-tRNA synthetase (PheRS) within a plantcell, particularly when the PheRS is expressed within the mitochondriaand/or chloroplast, confers resistance of the plant to meta-tyrosine.This resistance is due to the ability of the introduced bacterial PheRSto hydrolyze the misacylated m-Tyr-tRNA^(Phe) and to prevent theincorporation of the non-protein amino acid into proteins.

Thus, according to one aspect, the present invention provides atransgenic plant comprising at least one cell comprising at least oneexogenous polynucleotide encoding an aminoacyl tRNA synthetase (aaRS) ora fragment thereof, the aaRS or a fragment thereof comprising an editingmodule capable of hydrolyzing tRNA misacylated with non-protein aminoacid analog, wherein the plant is resistant to the non-protein aminoacid analog and salts thereof.

In the context of the present invention, the term “resistant tonon-protein amino acid analog” refers to the ability of the transgenicplant to grow in a growth medium comprising the non-protein amino acidanalog in a concentration that significantly inhibits the growth of acorresponding non-transgenic plant. According to certain embodiments,growth inhibition is shown by at least one of reduced root length,reduced root radical, reduced root mass, reduced plant height, aberrantchange in a plant tissue morphology or color, reduced plant shoot massand/or number and any combination thereof. According to someembodiments, the isolated non-protein amino acid analog or a compositioncomprising same is added to the growth medium. According to otherembodiments, the non-protein amino acid analog is secreted to the growthmedium from a plant producing same.

According to certain embodiments, the non-protein amino acid analog ismeta-tyrosine (m-Tyr) compound and the aaRS is phenylalanyl-tRNAsynthetase (PheRS).

According to certain embodiments, the m-Tyr compound has a formula ofFormula I or a salt thereof:

Wherein

R₁ and R₂ are independently selected from the group consisting of H,sulfonate, sulfonamide, phosphonate, alkyl, alkenyl, alkynyl, alkoxy,alkoxycarbonyl, saccharide, cycloalkyl, heterocycloalkyl, aryl andheteroaryl, wherein each of the phosphonate, alkyl, alkenyl, alkynyl,alkoxy, alkoxycarbonyl, saccharide, cycloalkyl, heterocycloalkyl, aryl,and heteroaryl is either substituted or unsubstituted;

R₃ is selected from the group consisting of H, alkyl, alkenyl, alkynyl,alkoxy, alkoxycarbonyl, saccharide, cycloalkyl, heterocycloalkyl, aryl,and heteroaryl, wherein each of the alkyl, alkenyl, alkynyl, alkoxy,alkoxycarbonyl, saccharide, cycloalkyl, heterocycloalkyl, aryl, andheteroaryl is either substituted or unsubstituted;

X is selected from the group consisting of O and N—Y, wherein Y isselected from the group consisting of H, alkyl, alkenyl, alkynyl,alkoxy, alkoxycarbonyl, saccharide, cycloalkyl, heterocycloalkyl, aryl,and heteroaryl, wherein each of the alkyl, alkenyl, alkynyl, alkoxy,alkoxycarbonyl, saccharide, cycloalkyl, heterocycloalkyl, aryl, andheteroaryl is either substituted or unsubstituted;

R₄, R₅, R₆, and R₇ are independently selected from the group consistingof H, hydroxyl, halogen, amino, and nitro; and

R₈ and R₉ are independently selected from the group consisting of H,hydroxyl, halogen, amino, methyl, and halogenated methyl.

According to certain typical embodiments, the m-Tyr compound has theformula of Formula II:

According to certain currently typical embodiments, the PheRS isbacterial PheRS. Bacterial PheRS is known to be heterotetrameric,comprising two α and two β subunits. According to certain embodiments,the α- and β-subunits are encoded by a single polynucleotide. Accordingto other embodiments, each of the α- and β-subunits is encoded by aseparate polynucleotide. According to yet further embodiments, thebacterial PheRS comprises at least one β-subunit or a fragment thereofcomprising the editing module.

According to some embodiments, the bacterial PheRS is a heterotetramericbacterial PheRS selected from the group consisting of Escherichia coli(E. coli) PheRS and Thermus thermophilus PheRS.

According to certain embodiments, the E. Coli PheRS-α subunit is encodedby a polynucleotide having the nucleic acid sequence set forth in SEQ IDNO:1 and the E. Coli PheRS-β subunit is encoded by a polynucleotidehaving the nucleic acid sequence set forth in SEQ ID NO:2.

According to other embodiments, the E. Coli PheRS-α subunit comprisesthe amino acid sequence set forth in SEQ ID NO:3 and the E. Coli PheRS-βsubunit comprises the amino acid sequence set forth in SEQ ID NO:4.

According to other embodiments, the T. thermophilus PheRS-α subunitcomprises the amino acid sequence set forth in SEQ ID NO:5 and the T.thermophilus PheRS-β subunit comprises the amino acid sequence set forthin SEQ ID NO:6.

According to certain embodiments, the polynucleotide encoding the aaRSor a fragment thereof comprising the editing module further comprises anucleic acid sequence encoding a targeting peptide selected from thegroup consisting of a mitochondrial targeting peptide and a chloroplasttargeting peptide. The mitochondrial and chloroplast targeting peptidescan be the same or different. Typically, the polynucleotide is sodesigned that the encoded targeting peptide is fused at the aminoterminus (N-terminus) of the encoded aaRS polypeptide.

According to certain embodiments, the transgenic plant comprises acombination of the exogenous polynucleotide encoding the aminoacyl tRNAsynthetase (aaRS) or a fragment thereof further comprising the nucleicacid sequence encoding the mitochondrial targeting peptide and theexogenous polynucleotide encoding the aaRS or a fragment thereof furthercomprising the nucleic acid sequence encoding a chloroplast targetingpeptide. The chloroplast targeting peptide and the mitochondrialtargeting peptide can be the same or different.

According to certain embodiments, the mitochondrial and the chloroplasttargeting peptides are encoded by the nucleic acid sequence set forth inSEQ ID NO:7 and have the amino acid sequence set forth in SEQ ID NO:8.

According to yet other embodiments, the polynucleotides of the presentinvention are incorporated in a DNA construct enabling their expressionin the plant cell. According to one embodiment, the DNA constructcomprises at least one expression regulating element selected from thegroup consisting of a promoter, an enhancer, an origin of replication, atranscription termination sequence, a polyadenylation signal and thelike.

According to some embodiments, the DNA construct comprises a promoter.The promoter can be constitutive, induced or tissue specific promoter asis known in the art. Each possibility represents a separate embodimentof the present invention. According to some embodiments, the promoter isa constitutive promoter operable in a plant cell. According to otherembodiments, the promoter is root specific promoter. According tofurther embodiments, the DNA construct further comprises transcriptiontermination and polyadenylation sequence signals.

Optionally, the DNA construct further comprises a nucleic acid sequenceencoding a detection marker enabling a convenient selection of thetransgenic plant. According to certain currently typical embodiments,the detection marker is selected from the group consisting of apolynucleotide encoding a protein conferring resistance to antibiotic; apolynucleotide encoding a protein conferring resistance to herbicide anda combination thereof.

The present invention also encompasses seeds of the transgenic plant,wherein plants grown from said seeds are resistant to phytotoxicnon-protein amino acid analog, particularly to m-Tyr. The presentinvention further encompasses fruit, leaves or any part of thetransgenic plant, as well as tissue cultures derived thereof and plantsregenerated therefrom.

According to yet another aspect, the present invention provides a methodfor producing a transgenic plant resistant to phytotoxic non-proteinamino acid analog or a salt thereof, comprising (a) transforming a plantcell with at least one exogenous polynucleotide encoding an aminoacyltRNA synthetase (aaRS) or a fragment thereof comprising an editingmodule, the editing module capable of hydrolyzing non-proteinaminoacylated tRNA; and (b) regenerating the transformed cell into atransgenic plant resistant to the phytotoxic non-protein amino acidanalog or a salt thereof.

The exogenous polynucleotide(s) encoding the aminoacyl tRNA synthetase(aaRS) or a fragment thereof comprising the editing module, capable ofhydrolyzing non-protein aminoacylated tRNA according to the teachings ofthe present invention can be introduced into a DNA construct to includethe entire elements necessary for transcription and translation asdescribed above, such that the polypeptides are expressed within theplant cell.

Transformation of plants with a polynucleotide or a DNA construct may beperformed by various means, as is known to one skilled in the art.Common methods are exemplified by, but are not restricted to,Agrobacterium-mediated transformation, microprojectile bombardment,pollen mediated transfer, plant RNA virus mediated transformation,liposome mediated transformation, direct gene transfer (e.g. bymicroinjection) and electroporation of compact embryogenic calli.According to one embodiment, the transgenic plants of the presentinvention are produced using Agrobacterium mediated transformation.

Transgenic plants comprising the exogenous polynucleotides encoding aaRSor a fragment thereof comprising the editing module according to theteachings of the present invention may be selected employing standardmethods of molecular genetics, as are known to a person of ordinaryskill in the art. According to certain embodiments, the transgenicplants are selected according to their resistance to an antibiotic orherbicide. According to one embodiment, the antibiotic serving as aselectable marker is one of the group consisting of cefotaxime,vancomycin and kanamycin. According to another embodiment, the herbicideserving as a selectable marker is the non-selective herbicideglufosinate-ammonium (BASTA®).

According to yet other embodiments, the transgenic plants of theinvention are selected based on their resistance to the phytotoxicnon-protein amino acid analog or salts thereof.

Any plant can be transformed with the polynucleotides of the presentinvention to produce the transgenic plants resistant to the presence ofphytotoxic non-protein amino acid analog, particularly m-Tyr or a saltthereof in the plant growth medium. According to typical embodiments,the plant is a crop plant or an ornamental plant.

Other objects, features and advantages of the present invention willbecome clear from the following description and drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-1B show the aminoacylation of tRNA^(Phe) with native andnon-protein amino acids and specific deacylation of mischarged product.FIG. 1A: Aminoacylation of E. coli tRNA^(Phe) transcript (1.2 μM) withPhe or m-Tyr by human mitochondrial (Hsmt)PheRS (210 nM) or Thermusthermophilus (Tt)PheRS (24 nM) analyzed by electrophoresis in 8%denaturing gel at acidic conditions (0.1 M Na-acetate, pH 5). FIG. 1B:Specific deacylation of m-Tyr-tRNA^(Phe) . E. coli tRNA^(Phe) transcript(1.2 μM) was aminoacylated with Phe (25 μM), m-Tyr (125 μM) or Tyr (1mM) by HsmtPheRS (250 nM in experiments with Phe and m-Tyr, or 500 nM inexperiments with Tyr) for 5 min; then the reaction was continued afteraddition (shown by arrows) of TtPheRS (16 nM), E. coli (Ec)PheRS (48 nM)or HsctPheRS (32 nM) (retrieved from Klipcan L. et al. 2009, ibid).

FIG. 2 shows the phenotypes of wild type and transgenic lines of A.Taliana. Root growth of Wt (wild type), Cyt (transgenic plant containingcytosol localized bacterial PheRS) and Dual (transgenic plant containingplastids localized bacterial PheRS). Upper panels: samples grown onmedia containing 20 μM m-Tyrosine. Bottom panels: non-treated samples.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides transgenic plants that are resistant tothe presence of a phytotoxic non-protein amino acid in the growth mediumsuch that the growth of the resistant plant is essentially not affectedby the phytotoxic amino acid. The present invention further providesmeans and method for producing the transgenic plants of the invention.According to certain embodiments, the phytotoxic non-protein amino acidis a meta-tyrosine (m-Tyr) compound or a salt thereof.

DEFINITIONS

The terms “aminoacyl tRNA synthetase” or “aaRS” are used herein as iscommon in the background art. aaRS is an enzyme that catalyzes theesterification of a specific amino acid or its precursor to one of allits compatible cognate tRNAs to form an aminoacyl-tRNA. The editingmodule of aaRS has evolved to correct misacylation of non-cognate aminoacids to the tRNA, which result in mistranslation of the genetic code.The editing module is capable of hydrolyzing the ester linkage betweenthe non-cognate amino acid and the tRNA. The term “fragment thereof”when used with reference to the aaRS enzyme refers to a fragment of theenzyme which preserves its catalytic activity and further comprises theenzyme editing module that is capable of hydrolyzing a non-protein aminoacid miscaylated to the tRNA.

The terms “non-protein amino acid” and “non-protein amino acid analog”are used herein interchangeably and refer to amino acids not included inthe set of the 22 canonical amino acids as is common in the backgroundart.

The term “plant” is used herein in its broadest sense. It includes, butis not limited to, any species of woody, herbaceous, perennial or annualplant. It also refers to a plurality of plant cells that are largelydifferentiated into a structure that is present at any stage of aplant's development. Such structures include, but are not limited to, aroot, stem, shoot, leaf, flower, petal, fruit, etc.

As used herein, the term “growth medium” refers to any medium that canbe used to support growth of a plant, and can include, withoutlimitation, various types of soils or plant nutrient media. Suitableexamples of soils include, without limitation, natural soil andartificial soil.

The terms “polynucleotide”, “polynucleotide sequence”, “nucleic acidsequence”, and “isolated polynucleotide” are used interchangeablyherein. These terms encompass nucleotide sequences and the like. Apolynucleotide may be a polymer of RNA or DNA or hybrid thereof, that issingle- or double-stranded, linear or branched, and that optionallycontains synthetic, non-natural or altered nucleotide bases. The termsalso encompass RNA/DNA hybrids.

The term “construct” as used herein refers to an artificially assembledor isolated nucleic acid molecule which includes the gene of interest.In general a construct may include the gene or genes of interest, amarker gene which in some cases can also be the gene of interest andappropriate regulatory sequences. It should be appreciated that theinclusion of regulatory sequences in a construct is optional, forexample, such sequences may not be required in situations where theregulatory sequences of a host cell are to be used. The term constructincludes vectors but should not be seen as being limited thereto.

The term “operably linked” refers to the association of nucleic acidsequences on a single nucleic acid fragment so that the function of oneis regulated by the other. For example, a promoter is operably linkedwith a coding sequence when it is capable of regulating the expressionof that coding sequence (i.e., that the coding sequence is under thetranscriptional control of the promoter). Coding sequences can beoperably linked to regulatory sequences in a sense or antisenseorientation.

The terms “promoter element,” “promoter,” or “promoter sequence” as usedherein, refer to a DNA sequence that is located at the 5′ end (i.e.precedes) the protein coding region of a DNA polymer. The location ofmost promoters known in nature precedes the transcribed region. Thepromoter functions as a switch, activating the expression of a gene. Ifthe gene is activated, it is said to be transcribed, or participating intranscription. Transcription involves the synthesis of mRNA from thegene. The promoter, therefore, serves as a transcriptional regulatoryelement and also provides a site for initiation of transcription of thegene into mRNA. Promoters may be derived in their entirety from a nativegene, or be composed of different elements derived from differentpromoters found in nature, or even comprise synthetic DNA segments. Itis understood by those skilled in the art that different promoters maydirect the expression of a gene in different tissues or cell types, orat different stages of development, or in response to differentenvironmental conditions. It is further recognized that since in mostcases the exact boundaries of regulatory sequences have not beencompletely defined, DNA fragments of some variation may have identicalpromoter activity. Promoters which cause a gene to be expressed in mostcell types at most times are commonly referred to as “constitutivepromoters”. New promoters of various types useful in plant cells areconstantly being discovered; numerous examples may be found in Okamuro JK and Goldberg R B (1989) Biochemistry of Plants 15:1-82.

As used herein, the term an “enhancer” refers to a DNA sequence whichcan stimulate promoter activity, and may be an innate element of thepromoter or a heterologous element inserted to enhance the level ortissue-specificity of a promoter.

The term “expression”, as used herein, refers to the production of afunctional end-product e.g., an mRNA or a protein.

The term “transgenic” when used in reference to a plant or seed (i.e., a“transgenic plant” or a “transgenic seed”) refers to a plant or seedthat contains at least one exogenous transcribeable polynucleotide inone or more of its cells. The term “transgenic plant material” refersbroadly to a plant, a plant structure, a plant tissue, a plant seed or aplant cell that contains at least one exogenous polynucleotide in atleast one of its cells. The exogenous polynucleotide can be a plantendogenous polynucleotide located at a different site or under adifferent regulation compared to the wild type situation, or aheterologous polynucleotide isolated from a different organism. A“transgenic plant” and a “corresponding non transgenic plant” as usedherein refer to a plant comprising at least one cell comprising anexogenous transcribeable polynucleotide and to a plant of the same typelacking said exogenous transcribeable polynucleotide.

The terms “transformants” or “transformed cells” include the primarytransformed cell and cultures derived from that cell regardless to thenumber of transfers. All progeny may not be precisely identical in DNAcontent, due to deliberate or inadvertent mutations. Mutant progeny thathave the same functionality as screened for in the originallytransformed cell are included in the definition of transformants.

Transformation of a cell may be stable or transient. The term “transienttransformation” or “transiently transformed” refers to the introductionof one or more exogenous polynucleotides into a cell in the absence ofintegration of the exogenous polynucleotide into the host cell's genome.Transient transformation may be detected by, for example, enzyme-linkedimmunosorbent assay (ELISA), which detects the presence of a polypeptideencoded by one or more of the exogenous polynucleotides. Alternatively,transient transformation may be detected by detecting the activity ofthe protein (e.g. glucuronidase) encoded by the exogenouspolynucleotide.

The term “transient transformant” refers to a cell which has transientlyincorporated one or more exogenous polynucleotides. In contrast, theterm “stable transformation” or “stably transformed” refers to theintroduction and integration of one or more exogenous polynucleotidesinto the genome of a cell. Stable transformation of a cell may bedetected by Southern blot hybridization of genomic DNA of the cell withnucleic acid sequences which are capable of binding to one or more ofthe exogenous polynucleotides. Alternatively, stable transformation of acell may also be detected by enzyme activity of an integrated gene ingrowing tissue or by the polymerase chain reaction of genomic DNA of thecell to amplify exogenous polynucleotide sequences. The term “stabletransformant” refers to a cell which has stably integrated one or moreexogenous polynucleotides into the genomic or organellar DNA. It is tobe understood that a plant or a plant cell transformed with the nucleicacids, constructs and/or vectors of the present invention can betransiently as well as stably transformed. The terms “polypeptide,”“peptide” and “protein” are used interchangeably herein to refer to apolymer of amino acid residues. The terms apply to amino acid polymersin which one or more amino acid residue is an artificial chemicalanalogue of a corresponding naturally occurring amino acid, as well asto naturally occurring amino acid polymers.

Among thousands known non-protein amino acids, about 300 are found inplants. Many of them are structurally similar to those considered asregular amino-acid substrates of aminoacyl tRNA synthetases (aaRSs).Amino acid side-chain modifications may be generated in vivo by reactiveoxygen species (ROS) such as hydroxyl radicals and superoxide anions.Very often the modifications are associated with production of one ormore hydroxyl group in para-, meta- or ortho-positions on the aromaticring of phenylalanine and tyrosine. However, the pathways of ROS-damagedamino acids incorporation into polypeptide chains remained unclear,taking into account editing activity of aaRSs.

The present invention now shows that (i) mitochondrial and cytoplasmicphenylalanyl-tRNA synthetases (defined HsmtPheRS and HsctPheRS,respectively) catalyze direct attachment of m-Tyr to tRNA^(Phe), therebyopening the way for delivery of the misacylated tRNA to the ribosome andincorporation of m-Tyr into eukaryotic proteins; and (ii) the presenceof bacterial PheRS in mitochondria and/or chloroplast induces plantresistance to m-Tyr. These finding form the basis for developing systemsof non-protein amino acids herbicides and plants resistant to theseherbicides.

According to one aspect, the present invention provides a transgenicplant comprising at least one cell comprising at least one exogenouspolynucleotide encoding an aminoacyl tRNA synthetase (aaRS) or afragment thereof, the aaRS or a fragment thereof comprising an editingmodule capable of hydrolyzing tRNA misacylated with non-protein aminoacid analog, wherein the plant is resistant to the non-protein aminoacid analog and salts thereof.

The teachings of the present invention are exemplified by the productionof transgenic plants expressing a bacterial phenylalanyl-tRNA synthetase(PheRS), that are resistant to the phytotoxic effect of m-Tyr compoundsand salts thereof. However, it is to be explicitly understood that thescope of the present invention encompasses any combination of aphytotoxic non-protein amino acid and aminoacyl tRNA synthetase (aaRS)or a fragment thereof, as long as the aaRS or its fragment comprises anediting module capable of hydrolyzing the non-protein amino acid fromthe tRNA.

The aaRS can be a native enzyme having an efficient editing activity asexemplified herein for E. coli PheRS. Alternatively, the aaRS can begenetically modified as to induce or increase the editing activity. Thesignificant plasticity of the synthetic and editing sites of aaRSs,particularly PheRS and minor changes in their stereo-chemicalorganization, can be used for designing the architecture of these sitesto change the binding affinity towards the small ligands or to controlhydrolytic activity towards misacylated tRNAs (Kotik-Kogan, O., Moor etal., 2005. Structure 13, 1799-1807; Fishman, R. et al. 2001. Actacrystallographica 57, 1534-1544). The exogenous aaRS, which ispreferably located within the mitochondrion and chloroplast cellularorganelles can repair the mistakes incorporated into proteins by thewild type aaRS enzymes using the extra-editing activity, and/or chelatethe harmful amino acid analog and prevent its incorporation into theproteins.

Cloning of a polynucleotide encoding the aaRS can be performed by anymethod as is known to a person skilled in the art. Various DNAconstructs may be used to express the aaRS in a desired plant.

The present invention provides a DNA construct or an expression vectorcomprising a polynucleotide encoding aaRS, which may further compriseregulatory elements, including, but not limited to, a promoter, anenhancer, and a termination signal.

Among the most commonly used promoters are the nopaline synthase (NOS)promoter (Ebert et al., 1987 Proc. Natl. Acad. Sci. U.S.A.84:5745-5749), the octapine synthase (OCS) promoter, caulimoviruspromoters such as the cauliflower mosaic virus (CaMV) 19S promoter(Lawton et al., 1987 Plant Mol. Biol. 9:315-324), the CaMV 35S promoter(Odell et al., 1985 Nature 313:810-812), and the figwort mosaic virus35S promoter, the light inducible promoter from the small subunit ofrubisco, the Adh promoter (Walker et al., 1987 Proc Natl Aca. Sci U.S.A.84:6624-66280, the sucrose synthase promoter (Yang et al., 1990 Proc.Natl. Acad. Sci. U.S.A. 87:4144-4148), the R gene complex promoter(Chandler et al., 1989. Plant Cell 1:1175-1183), the chlorophyll a/bbinding protein gene promoter, etc. Other commonly used promoters arethe promoters for the potato tuber ADPGPP genes, the sucrose synthasepromoter, the granule bound starch synthase promoter, the glutelin genepromoter, the maize waxy promoter, Brittle gene promoter, and Shrunken 2promoter, the acid chitinase gene promoter, and the zein gene promoters(15 kD, 16 kD, 19 kD, 22 kD, and 27 kD; Perdersen et al. 1982 Cell29:1015-1026). A plethora of promoters is described in InternationalPatent Application Publication No. WO 00/18963. According to certaincurrently typical embodiments, the construct of the present inventioncomprises the constitutive CaMV 35S promoter.

The “3′ non-coding sequences” refer to DNA sequences located downstreamof a coding sequence and include polyadenylation recognition sequencesand other sequences encoding regulatory signals capable of affectingmRNA processing or gene expression. The polyadenylation signal isusually characterized by affecting the addition of polyadenylic acidtracts to the 3′ end of the mRNA precursor. The use of different 3′non-coding sequences is exemplified by Ingelbrecht I L et al. (1989.Plant Cell 1:671-680).

In particular embodiments of the present invention, four clones of E.coli PheRS subunits: EcPheRSα, mtp-EcPheRSα, EcPheRSβ, and mtp-EcPheRSβwere prepared under the regulation of the constitutive promoter ³⁵S andcarried resistance to the non-selective herbicide glufosinate-ammonium(BASTA®) (EcPheRSα and mtp-EcPheRSα) or kanamycin (EcPheRSβ, andmtp-EcPheRSβ). The mtp-EcPheRSα and mtp-EcPheRSβ further included dual(mitochondrial and chloroplast) targeting peptide. The clones weretransformed into Arabidopsis thaliana plants (Columbia (Col-0) ecotype)via Agrobacterium tumefaciens.

Those skilled in the art will appreciate that the various components ofthe nucleic acid sequences and the transformation vectors described inthe present invention are operatively linked, so as to result inexpression of said nucleic acid or nucleic acid fragment. Techniques foroperatively linking the components of the constructs and vectors of thepresent invention are well known to those skilled in the art. Suchtechniques include the use of linkers, such as synthetic linkers, forexample including one or more restriction enzyme sites.

According to yet another aspect, the present invention provides a methodfor producing a transgenic plant resistant to phytotoxic non-proteinamino acid analog or a salt thereof, comprising (a) transforming a plantcell with at least one exogenous polynucleotide encoding an aminoacyltRNA synthetase (aaRS) or a fragment thereof comprising an editingmodule capable of hydrolyzing tRNA aminoacylated with non-protein aminoacid; and (b) regenerating the transformed cell into a transgenic plantresistant to the phytotoxic non-protein amino acid analog or a saltthereof.

Methods for transforming a plant cell with nucleic acids sequencesaccording to the present invention are known in the art. As used hereinthe term “transformation” or “transforming” describes a process by whicha foreign DNA, such as a DNA construct, enters and changes a recipientcell into a transformed, genetically modified or transgenic cell.Transformation may be stable, wherein the nucleic acid sequence isintegrated into the plant genome and as such represents a stable andinherited trait, or transient, wherein the nucleic acid sequence isexpressed by the cell transformed but is not integrated into the genome,and as such represents a transient trait. According to typicalembodiments the nucleic acid sequence of the present invention is stablytransformed into a plant cell.

There are various methods of introducing foreign genes into bothmonocotyledonous and dicotyledonous plants (for example, Potrykus I.1991. Annu Rev Plant Physiol Plant Mol Biol 42:205-225; Shimamoto K. etal., 1989. Nature 338:274-276).

The principal methods of the stable integration of exogenous DNA intoplant genomic DNA includes two main approaches:

Agrobacterium-mediated gene transfer: The Agrobacterium-mediated systemincludes the use of plasmid vectors that contain defined DNA segmentswhich integrate into the plant genomic DNA. Methods of inoculation ofthe plant tissue vary depending upon the plant species and theAgrobacterium delivery system. A widely used approach is the leaf-discprocedure, which can be performed with any tissue explant that providesa good source for initiation of whole-plant differentiation (Horsch etal., 1988. Plant Molecular Biology Manual A5, 1-9, Kluwer AcademicPublishers, Dordrecht). A supplementary approach employs theAgrobacterium delivery system in combination with vacuum infiltration.The Agrobacterium system is especially useful in the generation oftransgenic dicotyledenous plants.

Direct DNA uptake: There are various methods of direct DNA transfer intoplant cells. In electroporation, the protoplasts are briefly exposed toa strong electric field, opening up mini-pores to allow DNA to enter. Inmicroinjection, the DNA is mechanically injected directly into the cellsusing micropipettes. In microparticle bombardment, the DNA is adsorbedon microprojectiles such as magnesium sulfate crystals or tungstenparticles, and the microprojectiles are physically accelerated intocells or plant tissues.

According to certain embodiments, transformation of the DNA constructsof the present invention into a plant cell is performed usingAgrobacterium system.

The transgenic plant is then grown under conditions suitable for theexpression of the recombinant DNA construct or constructs. Expression ofthe recombinant DNA construct or constructs reduce the plantsusceptibility to non-protein amino acid analogs, particularly tom-tyrosine.

The regeneration, development and cultivation of plants from singleplant protoplast transformants or from various transformed explants iswell known in the art (Weissbach and Weissbach, In.: Methods for PlantMolecular Biology, (Eds.), 1988 Academic Press, Inc., San Diego,Calif.). This regeneration and growth process typically includes thesteps of selection of transformed cells, culturing those individualizedcells or tissues through the usual stages of embryonic developmentthrough the rooted plantlet stage. Transgenic embryos and seeds aresimilarly regenerated. The resulting transgenic rooted shoots arethereafter planted in an appropriate plant growth medium such as soil.

Selection of transgenic plants transformed with a nucleic acid sequenceof the present invention as to provide transgenic plants comprising theexogenous aaRS is performed employing standard methods of moleculargenetics, known to a person of ordinary skill in the art. According tocertain embodiments, the nucleic acid sequence further comprises anucleic acid sequence encoding a product conferring resistance toantibiotic, and thus transgenic plants are selected according to theirresistance to the antibiotic. According to some embodiments, theantibiotic serving as a selectable marker is one of the aminoglycosidegroup consisting of paromomycin and kanamycin. According to additionalembodiments, the nucleic acid sequence further comprises a nucleic acidsequence encoding a product conferring resistance to an herbicide,including, but not limited to, resistant to the non-selective herbicideglufosinate-ammonium (BASTA®). Methods for detecting the presence and/orexpression of the exogenous polynucleotide within the transgenic plantsare also known to a person skilled in the art, and include, for example,PCR, Northern and Southern hybridization. As exemplified herein, thefinal confirmation for obtaining a transgenic plant of the presentinvention is obtained by growing the transgenic plants comprising theexogenous polynucleotide in a medium comprising phytotoxic concentrationof the non-protein amino acid. Only plants expressing an active aaRS ora fragment thereof having the editing module can normally grow underthese conditions.

Also within the scope of this invention are seeds or plant partsobtained from the transgenic plants that maintain the resistance tophytotoxic concentration of the non-protein amino acid. Plant partsinclude differentiated and undifferentiated tissues, including but notlimited to, roots, stems, shoots, leaves, pollen, seeds, tumor tissue,and various forms of cells and culture such as single cells,protoplasts, embryos, and callus tissue. The plant tissue may be in theplant or in organ, tissue or cell culture.

The following examples are presented in order to more fully illustratesome embodiments of the invention. They should, in no way be construed,however, as limiting the broad scope of the invention. One skilled inthe art can readily devise many variations and modifications of theprinciples disclosed herein without departing from the scope of theinvention.

EXAMPLES Material and Methods

Four clones of E. coli PheRS subunits: EcPheRSα, mtp-EcPheRSα, EcPheRSβ,and mtp-EcPheRSβ were prepared under the regulation of the constitutivepromoter 35S and carried resistance to BASTA (EcPheRSα and mtp-EcPheRSα)or kanamycin (EcPheRSβ, and mtp-EcPheRSβ). The mtp-EcPheRSα andmtp-EcPheRSβ contained dual (mitochondrial and chloroplast) targetingpeptide. The clones were transformed into Arabidopsis thaliana plants(Columbia (Col-0) ecotype) via Agrobacterium tumefaciens.

For transformation, plants were grown in a growth room under controlledconditions (temperature 22° C., 8 hours light) for 30 days and thentransformed as described hereinbelow. Wild type and transformed seedswere sterilized, cold-treated, and germinated on sterile MS media withor without antibiotic. After germination the plants were planted in potsand transferred to the growth room (22° C. 16 hours light).

Agrobacterium Infiltration Transformation

Agrobacterium tumefaciens strain ABI harboring the binary vectors pART27or pMLBart was used for transformation. Both vectors contain the nptIIgene as a selectable marker. Small scale Agrobacterium cultures weregrown in liquid LB medium with appropriate antibiotics at 28° C.overnight. The small scale cultures were then diluted 50-fold into LBmedium with appropriate antibiotics for large scale overnight cultures.Cells were then harvested by centrifugation at 5000 r.p.m. (about 3000g) for 15 min, and re-suspended in infiltration medium to an OD600 of0.8.

Inoculations were performed by dipping aerial parts of the plants for 30second in 300 ml of a solution containing 5% (w/v) Sucrose, 10 mM MgCl₂,re-suspended Agrobacterium cells from a 200-ml overnight culture, and0.05% of the surfactant (Silwet L-77). After the inoculation plants wereleft in a low-light or dark location and covered with a transparentplastic dome to maintain humidity; the dome was removed and the plantsreturned to the growth chamber 12 to 24 h after inoculation. Transformedplants were kept in the greenhouse and seeds were harvested upon fullmaturation.

Plant Selection

The seeds were germinated on soil and transgenic plants were selected byspraying with 0.1% BASTA® herbicide in the greenhouse. Spraying wasperformed one week after germination and repeated four times at two-dayintervals. Transgenic plants were readily identified at the end of theBASTA® selection. While such plants continued to grow and remainedgreen, the untransformed plants remained small, became white and diedtwo weeks after selection. For selection positive plant containingkanamycin resistance, seeds were screened in MS medium supplemented with50 mg/ml kanamycin.

Crosses

After homozygote plant for each (α- or β-) subunits of PheRS wereobtained, they were subjected to crosses. The plants used as femaleswere hand emasculated. Anthers from freshly opened flowers of donorplants were harvested and pollination was performed by touching theanthers onto the stigmas of the emasculated plants. The pollinatedflowers were labeled and any remaining opened or unopened flowers fromthe same plant were removed to avoid any confusion at harvest. Theselection of positive plants containing both subunits of PheRS was doneas described in the “Plant Selection” section hereinabove.

The m-Tyr Resistance

To assess effects of m-Tyr on Arabidopsis root growth, 20 m of m-Try wasadded to MS medium. Arabidopsis seeds were sterilized by shaking in 30%bleach, 0.3% Triton X-100 for 10 min, followed by three rinses withsterile distilled water. Petri dishes with seeds on agar medium werecold-stratified for 72 h at 4° C., and were subsequently placedvertically in green-house at 23° C., under 16:8 h light/dark cycle.After 7 days of growth, the root length of the plant was analyzed.

Example 1 The Effect of Bacterial PheRS Expression on ArabidopsisResistance to m-Tyr

The bacterial PheRS genes described in the “Material and Methods”section hereinabove were expressed under the control of the constitutive35S CaMV promoter. A transit peptide was appended to N-terminus ofEcPheRS-α and EcPheRS-β subunits of the bacterial enzyme in order todirect them into the mitochondria and chloroplast of Arabidopsisthaliana. The second constructs pair including PheRS-α and PheRS-βlacked the transit peptides. Thus, four different constructs weretransformed into Arabidopsis thaliana, and homozygote self-pollinatedplants were generated as described hereinabove. Each line was furthercrossed to create plants containing heterodimeric EcPheRS possessingediting activity localized in cytoplasm (cyt-PheRS) and heterodimericEcPheRS localized in plant mitochondria and chloroplast (mtp-PheRS).Several independent transgenic lines were obtained, and their resistanceto m-Tyr was analyzed. Resistance to m-Tyr was examined by growingwild-type, cyt-PheRS and mtp-PheRS Arabidopsis thaliana lines in Petridishes containing 20 M m-Tyr in the growth media. Same lines grown onuntreated media served as a control. The resistance to m-Tyr was alreadyobserved at the F2 generation. Resistance was found to be much moreprofound for line containing mtp-PheRS (FIG. 2). It can be seen thatwhile the roots of wild type plants didn't develop at 20 M m-Tyr theroots of lines containing mtp-PheRS developed up to the half of thelength of the non-treated plants. The roots of cyt-PheRS expressing lineare less developed compared to the line containing mtp-PheRS. It is tobe noted that the growth of the transgenic Arabidopsis plants grownunder normal conditions was unaffected considerably by the presence ofbacterial PheRS in the cytoplasm or organelles (FIG. 2).

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without undue experimentation and withoutdeparting from the generic concept, and, therefore, such adaptations andmodifications should and are intended to be comprehended within themeaning and range of equivalents of the disclosed embodiments. It is tobe understood that the phraseology or terminology employed herein is forthe purpose of description and not of limitation. The means, materials,and steps for carrying out various disclosed functions may take avariety of alternative forms without departing from the invention.

What is claimed is:
 1. A transgenic plant comprising at least one cellcomprising at least one exogenous polynucleotide encoding an aminoacyltRNA synthase (aaRS) or a fragment thereof, the aaRS or fragment thereofcomprising an editing module capable of hydrolyzing tRNA misacylatedwith non-protein amino acid analog, wherein the plant is resistant tothe non-protein amino acid analog and salts thereof.
 2. The transgenicplant of claim 1, wherein said plant grows in a medium containing thenon-protein amino acid or salt thereof in a concentration thatsignificantly inhibits the growth of a corresponding non-transgenicplant.
 3. The transgenic plant of claim 3, wherein growth inhibition isshown by at least one of reduced root length, reduced root radical,reduced root mass, reduced plant height, aberrant change in a planttissue morphology or color, reduced plant shoot mass, reduced plantshoot number and any combination thereof.
 4. The transgenic plant ofclaim 1, wherein the non-protein amino acid analog is meta-tyrosine(m-Tyr) compound and the aaRS is phenylalanyl-tRNA synthetase (PheRS).5. The transgenic plant of claim 4, wherein the m-Tyr compound has aformula of Formula I or a salt thereof, Formula I having the followingformula:

wherein: R₁ and R₂ are independently selected from the group consistingof H, sulfonate, sulfonamide, phosphonate, alkyl, alkenyl, alkynyl,alkoxy, alkoxycarbonyl, saccharide, cycloalkyl, heterocycloalkyl, aryland heteroaryl, wherein each of the phosphonate, alkyl, alkenyl,alkynyl, alkoxy, alkoxycarbonyl, saccharide, cycloalkyl,heterocycloalkyl, aryl, and heteroaryl is either substituted orunsubstituted; R₃ is selected from the group consisting of H, alkyl,alkenyl, alkynyl, alkoxy, alkoxycarbonyl, saccharide, cycloalkyl,heterocycloalkyl, aryl, and heteroaryl, wherein each of the alkyl,alkenyl, alkynyl, alkoxy, alkoxycarbonyl, saccharide, cycloalkyl,heterocycloalkyl, aryl, and heteroaryl is either substituted orunsubstituted; X is selected from the group consisting of O and N—Y,wherein Y is selected from the group consisting of H, alkyl, alkenyl,alkynyl, alkoxy, alkoxycarbonyl, saccharide, cycloalkyl,heterocycloalkyl, aryl, and heteroaryl, wherein each of the alkyl,alkenyl, alkynyl, alkoxy, alkoxycarbonyl, saccharide, cycloalkyl,heterocycloalkyl, aryl, and heteroaryl is either substituted orunsubstituted; R₄, R₅, R₆, and R₇ are independently selected from thegroup consisting of H, hydroxyl, halogen, amino, and nitro; and R₈ andR₉ are independently selected from the group consisting of H, hydroxyl,halogen, amino, methyl, and halogenated methyl.
 6. The transgenic plantof claim 5, wherein the m-Tyr compound has a formula of Formula II,Formula II having the following formula:


7. The transgenic plant of claim 4, wherein the PheRS is aheterotetrameric bacterial PheRS composed of two PheRS-α and two PheRS-βstrands.
 8. The transgenic plant of claim 7, wherein the bacterial PheRSis selected from the group consisting of Escherichia coli (E. coli)PheRS and Thermus thermophilus PheRS.
 9. The transgenic plant of claim8, wherein the E. Coli PheRS-α is encoded by a polynucleotide having thenucleic acid sequence set forth in SEQ ID NO:1 and the E. Coli PheRS-βis encoded by a polynucleotide having the nucleic acid sequence setforth in SEQ ID NO:2.
 10. The transgenic plant of claim 8, wherein theE. Coli PheRS-α comprises the amino acid sequence set forth in SEQ IDNO:3; the E. Coli PheRS-β comprises the amino acid sequence set forth inSEQ ID NO:4; the T. thermophilus PheRS-α comprises the amino acidsequence set forth in SEQ ID NO:5 and the T. thermophilus PheRS-βcomprises the amino acid sequence set forth in SEQ ID NO:6.
 11. Thetransgenic plant of claim 1, wherein the polynucleotide encoding theaaRS or fragment thereof further comprises a nucleic acid sequenceencoding a targeting peptide selected from the group consisting of amitochondrial targeting peptide and a chloroplast targeting peptide. 12.The transgenic plant of claim 11, wherein said plant comprises acombination of (a) the polynucleotide encoding the aaRS or a fragmentthereof further comprising the nucleic acid sequence encoding amitochondrial targeting peptide and (b) the polynucleotide encoding theaaRS or a fragment thereof further comprising the nucleic acid sequenceencoding a chloroplast targeting peptide.
 13. A plant seed produced bythe transgenic plant of claim 1, wherein the seed is used for breeding atransgenic plant comprising at least one exogenous polynucleotideencoding an aminoacyl tRNA synthase (aaRS) or a fragment thereof havingan editing module capable of hydrolyzing tRNA misacylated withnon-protein amino acid analog, wherein the transgenic plant is resistantto the non-protein amino acid analog and salts thereof.
 14. A tissueculture comprising at least one transgenic cell of the plant of claim 1or a protoplast derived therefrom, wherein the tissue cultureregenerates a transgenic plant comprising at least one exogenouspolynucleotide encoding an aminoacyl tRNA synthase (aaRS) or a fragmentthereof having an editing module capable of hydrolyzing tRNA misacylatedwith non-protein amino acid analog, the transgenic plant is resistant tothe non-protein amino acid analog and salts thereof.
 15. A method forproducing a transgenic plant resistant to phytotoxic non-protein aminoacid analog or a salt thereof, the method comprising the steps of: (a)transforming a plant cell with at least one exogenous polynucleotideencoding an aminoacyl tRNA synthetase (aaRS) or a fragment thereof theaaRS or fragment thereof comprising an editing module capable ofhydrolyzing non-protein aminoacylated tRNA; and (b) regenerating thetransformed cell into a transgenic plant resistant to the phytotoxicnon-protein amino acid analog or a salt thereof.
 16. The method of claim15, wherein the non-protein amino acid analog is meta-tyrosine (m-Tyr)compound and the aaRS is phenylalanyl-tRNA synthetase (PheRS).
 17. Themethod of claim 16, wherein the PheRS is a heterotetrameric bacterialPheRS composed of two PheRS-α and two PheRS-β strands.
 18. The method ofclaim 17, wherein the bacterial PheRS is Escherichia coli (E. coli)PheRS or Thermus thermophilus PheRS.
 19. The method of claim 18, whereinthe E. Coli PheRS-α is encoded by a polynucleotide having the nucleicacid sequence set forth in SEQ ID NO:1 and wherein the E. Coli PheRS-βis encoded by a polynucleotide having the nucleic acid sequence setforth in SEQ ID NO:2.
 20. The method of claim 18, wherein the E. ColiPheRS-α comprises the amino acid sequence set forth in SEQ ID NO:3; theE. Coli PheRS-β comprises the amino acid sequence set forth in SEQ IDNO:4; the T. thermophilus PheRS-α comprises the amino acid sequence setforth in SEQ ID NO:5 and the T. thermophilus PheRS-β comprises the aminoacid sequence set forth in SEQ ID NO:6.
 21. The method of claim 15,wherein the polynucleotide encoding the aaRS or fragment thereof furthercomprises a nucleic acid sequence encoding a targeting peptide selectedfrom the group consisting of a mitochondrial targeting peptide and achloroplast targeting peptide.
 22. The method of claim 21, wherein theplant cell is transformed with a combination of (a) the polynucleotideencoding the aaRS or a fragment thereof further comprising the nucleicacid sequence encoding a mitochondrial targeting peptide and (b) thepolynucleotide encoding the (aaRS) or a fragment thereof furthercomprising the nucleic acid sequence encoding a chloroplast targetingpeptide.
 23. A transgenic plant produced by the method of claim 15,wherein the plant is resistant to the phytotoxic non-protein amino acid.